Method for activating glowing cathodes or the like



Patented Jan. 24, 1933 UNITED STATES PATENT OFFICE WERNER ESPE, OIIBERLIN-CHARLOTT-ENBUBG, GERMANY, ASSIGNOB TO SIEMENS 86 HALSKE.AKTIENGESELLSCHAFT, OF SIEMENSSTADT NEAR BERLIN, GERMANY, A

GERMAN COMPANY METHOD FOR Ao'rIvA'rINe GLOWING CATHODES on THE LIKE NoDrawing. Application filed August 14, 1930, Serial No. 475,400, and inGermany August 19, 1929.

The invention relates to a method for activating glowing cathodes or thelike by means of metals of the alkaline earth group which are formedfrom chemical compounds of these metals in the tube.

The oxide paste cathode which, as well known, is produced from a pasteconsisting of alkaline earth oxides applied to the core has theadvantage of possessing an extraordinarily long life (5000 hours andmore) but shows however a relatively low activity (40 milliampere perwatt). This is due to the fact that during the formation process a thinlayer of pure alkaline earth metal is produced on the surface of thecathode by electrolysis which displaces itself automatically from theoxide base in the course of operation. Recently one has gone over todistilling over the earth alkaline metal in metallic form on the corefrom an electrode whereby a complete coating of the cathode surface withalkaline earth metal and a very high activity (about 120 milliampere perwatt) is obtained. In view of the fact however that the layers distilledon are very thin, the life of a cathode of this kind is considerablyshorter than that of the squirted or paste cathode (about 800 to 1000hours).

An object of this invention is the making of glowing cathodes or thelike which have both the high activity of distillation cathodes and thelong life of squirted or paste cathodes.

In accordance with the invention one of the alkaline earth metals, is inthe well known manner, applied to the oxide paste cathode, said metalbeing obtained froma compound which only decomposes above the maximumtemperature occurring in the tube during the formation process of theoxide paste cathode.

It was observed however that an unformed squirted cathode could not becoated with an alkaline earth metal, as on subsequent formation so muchgas escaped from the oathode that the alkaline earth metal distilled onwas oxidized again and its effect was thereby nullified. If, however,the oxide cathode is formed first, a high heating of the cathode and ahigh anode potential are necessary so that the other electrode on whichthe alkaline earth metal source is situated glows highly Before,however, completely terminating the formation this source must not beclosed. F or this reason it is not possi ble to use, for instance,azides of alkaline earth metals whichdeoompose at-approximately 180centigrade.

For appropriate reasons a mixture is used, 1

which consists of a compound of a metal of the alkaline earth group, forinstance, barium oxide and aluminium oran equivalent metal, forinstance, magnesium and which reacts only at temperatures over 1000whereby metallic barium forms.

For forming a glowing cathode in accordance with the invention one mayproceed in the following manner.

After evacuation, the squirted cathode ishighly heated and any availablecarbonate decomposed into the oxide. The forming is thereupon effectedwith anode potential in that gradually increasing anode potentials areone after the other applied to the grid or grids and the anode, wherebysimultaneously with the formation of the cathode both electrodes and thereaction mixture are raised to temperatures up to 1000 centigradeand canbe well de-gassed. If the emission of the cathode has attained thedesired degree the formation is terminated. After cooling of the tubehas been effected, the mixture applied to the anode or situated in aspecial container is ignited by heating for a short time at 1100 to 1200centi grade, in any well known manner, as by highfrequency light or heatrays which are concentrated through mirrors or lenses, whereupon thereaction proceeds further automatically, until all the 700 C. Thegradually evaporated alkaline earth metal is ionized by the electrons ofthe oxide cathode and the positive alkaline earth metal ions fly.directively to the negative cathode and accumulate thereon to a greaterextent than by ordinary temperature distillation Where the major portionof the alkaline earth metal would go to the cold glass *wall'ofthetubm;I .r The method in: accordance with the inven'@ tion oflers thisadvantage that the reaction temperature is substantially higher than thetemperature employed for de-gassing the metal parts and forming thecathodes so that thegasescohtained'in the metal parts of the electrodesand resulting on the formation of theioxide'paste cathode are removed bythe long before the metal formed the evacuating said enclosing vessel,heating said cathode to completely decompose said first compound to formthe oxide of said metal, simultaneously applying a potential betweensaid cathodeoand said electrode whereby said electrodeand said mixtureare out-gassed by electron bombardment, removing the liberated gasesfrom said vessel, removing said potent'ial, heating-f saidatmixture to;liberate-the free alkaline: earth: .therefnom, applying a negativepotentialtoisaid: cathode, and 7 simultaneously heating said electrodeto complletely transferisaid metal tosaid oxide cathiIn'witness whereof,I hereunto subscribe my name, this, 5th day of August, 1930. V

" p 1' WERNER ESPE.

reaction mixture. is over-distilled to thed formed cathode;

What is claimed is: '1'. In the manufacture of electron dischargefdevices comprising a cathode having a coating. of-barium carbonate, anelectrode adjacent said cathode, and'a mixture includ-.

ing barium oxide, and a reducing agent upon said electrode, the. methodwhich comprises heating, said carbonate to form barium oxde, applyingapotential between saidcathode I and said eleetrodewhereby said electrodeand said mixture are out-gassed by electron i bombardment, producing areaction in said mixture to form metallic barium, applying a y a bariumon said cathode.

V negative potentialto said cathode and'simultaneously heating saidelectrode to 1on- ,l izefsaidbarium, anddepositmg said lOlllZed 21 Inthe manufacture of electrode disi- I charge devlcescomprlsing a cathodehaving a U I coating of decomposable compoundsv of'alkaline earth metal,an electrode adjacent said 'cathOdeQand a reactionmixture having areaction temperature hi ghe'r than that atwhi ch said" compound isdecomposable carried by said electrode, the methodfwhich comprisesdecomposing saidcompound to form the oxline earth metal'thereon, lsaidcompound 'beingydeeomposableto form the oxide offsaid metalhan electrodeadjacent said cathode,

andia mixture including a compound of an alkaline earthmetaluponsaidelectrode, said mixture havinga reaction temperature high- I 1 erthan that 1 at which said first'compoundis decomposable, the methodWhichcomprises

